Integrated broadband optical couplers with robustness to manufacturing variation

ABSTRACT

An optical device is disclosed, including a phase delay, a first adiabatic coupler adapted to receive an input signal and adapted to be optically coupled to an input of the phase delay, and a second adiabatic coupler adapted to be optically coupled to an output of the phase delay. The second adiabatic coupler includes a first waveguide including a first portion optically coupled to the first output and including a first width, and a second waveguide including a second portion optically coupled to the second output and including a second width that is approximately equal to the first width.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 16/593,821, filed Oct. 4, 2019. The aforementioned relatedpatent application is herein incorporated by reference in its entirety.

TECHNICAL FIELD

Embodiments presented in this disclosure generally relate to fiber opticcommunications. More specifically, though not exclusively, embodimentsdisclosed herein relate to a broadband tap coupler.

BACKGROUND

In fiber-optic communications (e.g., a broadband fiber opticcommunication system), wavelength-division multiplexing (WDM) can beused to multiplex multiple optical carrier signals onto an opticalfiber. WDM uses different wavelengths of light to facilitate datacommunication over a fiber (e.g., transmitting data from a data sourceto a data recipient). A WDM system commonly uses a multiplexer at thetransmitter to join several signals together, and a demultiplexer at thereceiver to split them apart.

In many telecom and data communication applications (e.g., coarse WDM inthe O-band or dense WDM in the C-band), WDM uses an optical devicereferred to as a broadband tap coupler as a building block for opticalsignal routing and processing. As one example, some frameworks (e.g.,400G-FR4) use a lattice filter for de-multiplexing. A lattice filter, ingeneral, relies on cascaded Mach-Zehnder Interferometers (MZI) withbroadband tap couplers.

BRIEF DESCRIPTION OF THE DRAWINGS

So that the manner in which the above-recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate typicalembodiments and are therefore not to be considered limiting; otherequally effective embodiments are contemplated.

FIGS. 1A-1C are block diagrams illustrating a broadband tap coupler,according to one embodiment described herein.

FIG. 2 illustrates a prior art tap coupler, according to one embodimentdescribed herein.

FIG. 3 illustrates a prior art adiabatic coupler, according to oneembodiment described herein.

FIG. 4 illustrates a further adiabatic coupler, according to oneembodiment described herein.

FIG. 5 illustrates a tap coupler device, according to one embodimentdescribed herein.

FIG. 6 illustrates a further tap coupler device, according to oneembodiment described herein.

FIG. 7 illustrates a top down view of a structure for a tap couplerdevice, according to one embodiment described herein.

To facilitate understanding, identical reference numerals have beenused, where possible, to designate identical elements that are common tothe figures. It is contemplated that elements disclosed in oneembodiment may be beneficially used in other embodiments withoutspecific recitation.

DESCRIPTION OF EXAMPLE EMBODIMENTS Overview

Embodiments disclosed herein include an optical communication device.The optical device includes a phase delay and an adiabatic coupler. Theadiabatic coupler includes a first output and a second output. Theadiabatic coupler further includes a first waveguide including a firstportion optically coupled to the first output and a second portionadapted to be optically coupled to the phase delay. The adiabaticcoupler further includes a second waveguide including a third portionoptically coupled to the second output and a fourth portion adapted tobe optically coupled to an output of another adiabatic coupler. Thefirst portion includes a first width and the third portion includes asecond width approximately equal to the first width. The adiabaticcoupler is configured to produce a first output signal using the firstoutput and a second output signal using the second output, with aconstant relative phase difference between the first output signal andthe second output signal. The adiabatic coupler is further configured todivide an input signal to the optical communication device in an unevenpower distribution between the first output signal and the second outputsignal.

Embodiments further include an adiabatic coupler, including a firstoutput and a second output. The adiabatic coupler further includes afirst waveguide including a first portion optically coupled to the firstoutput and a second portion adapted to be optically coupled to a phasedelay. The adiabatic coupler further includes a second waveguideincluding a third portion optically coupled to the second output and afourth portion adapted to be optically coupled to an output of anotheradiabatic coupler. The first portion includes a first width and thethird portion includes a second width approximately equal to the firstwidth. The adiabatic coupler is included in an optical communicationdevice, and the adiabatic coupler is configured to produce a firstoutput signal using the first output and a second output signal usingthe second output, with a constant relative phase difference between thefirst output signal and the second output signal. The adiabatic coupleris further configured to divide an input signal to the opticalcommunication device in an uneven power distribution between the firstoutput signal and the second output signal.

Embodiments further include a fiber optic communication system,including a data source, a multiplexer, a demultiplexer, and a tapcoupler. The tap coupler includes a phase delay and an adiabaticcoupler. The adiabatic coupler includes a first output and a secondoutput. The adiabatic coupler further includes a first waveguideincluding a first portion optically coupled to the first output and asecond portion adapted to be optically coupled to the phase delay. Theadiabatic coupler further includes a second waveguide including a thirdportion optically coupled to the second output and a fourth portionadapted to be optically coupled to an output of another adiabaticcoupler. The first portion includes a first width and the third portionincludes a second width approximately equal to the first width. Theadiabatic coupler is configured to produce a first output signal usingthe first output and a second output signal using the second output,with a constant relative phase difference between the first outputsignal and the second output signal. The adiabatic coupler is furtherconfigured to divide an input signal to the tap coupler in an unevenpower distribution between the first output signal and the second outputsignal.

Example Embodiments

A tap coupler is an optical device that can be used in a fiber opticcommunication system. In general, a tap coupler intended for highbandwidth usage should be insensitive to a wide range of wavelengthsacross different communication bands. That is, the tap coupler shoulddistribute the input signal across the desired outputs, in the desiredfashion, regardless of the wavelengths included in the input signal.This allows the tap coupler to be used in a fiber optic communicationthat uses a large number of wavelength channels, facilitating higherdata bandwidth. Further, a tap coupler may generate a phase differencebetween outputs. It can also be important that this phase difference isconstant to allow for reliable operation in a high bandwidthenvironment.

In some circumstances, thickness variation during manufacturing canchange the output phase difference of the tap coupler, harmingreliability. In other circumstances, thickness variation duringmanufacturing can create cross-talk between communication channels, alsoharming reliability. This can be particularly problematic in integratedCMOS-based silicon photonics in a high bandwidth environment. Forexample, in high bandwidth environments broadband tap couplers mustcomply with stringent cross-talk requirements (e.g., 25 dB in 400G-FR4).A slight process variation during manufacturing can mean that a tapcoupler does not comply with these cross-talk requirements.

It is, therefore, beneficial when the tap coupler is both robust tomanufacturing variation in terms of bandwidth, by reducing (oreliminating) cross-talk across channels, and robust to manufacturingvariation in terms of phase difference, by generating a constant phasedifference. One more techniques disclosed herein relate to a broadbandtap coupler which is robust to manufacturing variation in terms of bothbandwidth and phase difference between output signals.

FIGS. 1A-1C are block diagrams illustrating a broadband tap coupler,according to one embodiment described herein. FIG. 1A is a block diagramillustrating a tap coupler 100, according to on embodiment describedherein. A tap coupler, in an embodiment, may be used to distribute powerbetween an optical input signal (e.g., laser light) and optical outputsignals, generating potentially different power distributions betweenoptical output signals.

As illustrated in FIG. 1A, the tap coupler 100 receives an input signal102 from a source 101 and outputs two output signals 112 and 114. Ingeneral, an optical coupler can be used to couple light from one (orseveral) inputs to one (or several) outputs. As illustrated in FIG. 1A,the tap coupler 100 distributes light received as the input signal 102to the output signals 112 and 114. This is merely one example, and anysuitable number of inputs and outputs can be used.

The output signal 112 is sent to a destination 113. The output signal114 is sent to a destination 115. In an embodiment, the input signal 102can be distributed evenly, or unevenly, among the output signals 112 and114. As an example of uneven distribution, the output signal 112 canrepresent 10% of the power of the input signal 102, while the outputsignal 114 represents 90% of the power of the input signal 102.Alternatively, as an example of even distribution, the output signals112 and 114 can each represent 50% of the power of the input signal 102.This distribution of the signal across output ports can be achieved innumerous ways. For example, as illustrated in FIGS. 1B-C, below, aMach-Zehnder Interferometer (MZI) can be used to distribute the signal.

FIG. 1B is a block diagram further illustrating the tap coupler 100,according to on embodiment described herein. In particular, FIG. 1Billustrates an MZI based tap coupler 100 which creates a phasedifference between output signals with phases 122 and 124. That is, thetap coupler 100 illustrated in FIG. 1B receives an input signal 102 andoutputs two output signals 112 and 114, just as illustrated in FIG. 1A.Again, the input signal 102 can be distributed evenly, or unevenly,among the output signals 112 and 114. Further, the input signal 102 andthe output signals 112 and 114 carry the same channels and the samedata.

As illustrated in FIG. 1B, however, the tap coupler 100 uses an MZI todistribute the input signal 102 between the output signals 112 and 114.This generates a phase difference between the output signals 112 and114. For example, the output signal 112 includes a phase 122, which isdifferent from the phase 124 for the output signal 114.

FIG. 1C is a further block diagram illustrating a tap couplerconfiguration 150, according to on embodiment described herein. In anembodiment, the tap coupler configuration 150 is again a Mach-ZehnderInterferometer (MZI) based tap coupler. The tap coupler configuration150 includes a first 2×2 coupler 162, phase delays 164A-B, and a second2×2 coupler 166. The 2×2 couplers 162 and 166 can each couple two inputsto two outputs. For example, the 2×2 coupler 162 couples the inputsignals 152 and 154 to the output signals 156 and 158. The 2×2 coupler166 couples the input signals 172 and 174 to the output signals 176 and178.

In an embodiment, an input signal 152 passes through the first 2×2coupler 162 and one (or both) of the phase delays 164A-B. The phasedelays 164A-B act to shift the phase of the output signals 156 and 158before entering the 2×2 coupler 166, as is known for MZI based tapcouplers. The 2×2 coupler 166 generates the output signals 176 and 178.In an embodiment, the tap coupler configuration 150 divides the inputsignal 152 into output signals 176 and 178. The output signals 176 and178 can be divided equally, or unequally.

The 2×2 couplers 162 and 166 can be any suitable 2×2 coupler. Forexample, the 2×2 couplers illustrated in FIGS. 2-4 may be used. Further,the phase delays 164A-B can be any suitable phase delay element (e.g.,any phase shifter suitable for existing MZI based tap couplers). FIG. 7,discussed below, describes one example phase delay structure suitablefor use as the phase delays 164A-B.

FIG. 2 illustrates a prior art tap coupler 200, according to oneembodiment described herein. The tap coupler 200 illustrates a known 2×2tap coupler configuration which is robust to manufacturing variance interms of phase difference between output signals, but which is notrobust to manufacturing variance in terms of bandwidth.

In an embodiment, the tap coupler 200 includes waveguides 210, each ofwhich has approximately the same width w. An input signal 202 isprovided to the tap coupler 200. The input signal passes through thewaveguides 210, generating output signals 222 and 224. In an embodiment,the output signal 222 represents x % of the power of the input signal202, while the output signal 224 represents y % of the power of theinput signal 202. That is, the output power of the output signals 222and 224 is not limited to 50/50.

The configuration of the tap coupler 200 is robust to manufacturingvariation in terms of phase difference: it generates output signals witha constant phase difference, regardless of minor variations in siliconthickness (e.g., as a result of manufacturing variance when forming thedevice). In particular, because the waveguides 210 have approximatelythe same width, the output signals 222 and 224 have a constant phasedifference of π/2 regardless of minor variations in thickness.

But the tap coupler 200 is not robust to manufacturing variation interms of bandwidth: its treatment of various communication channels isnot robust to thickness variation. As discussed above, modern broadbandfiber optic communication systems must be able to meet broad bandwidthrequirements. Manufacturing variances (e.g., variations in siliconthickness during manufacturing) in the tap coupler 200 can generatecross-talk across difference communication channels, harming reliabilityand potentially violating cross-talk and bandwidth requirements.

FIG. 3 illustrates a prior art adiabatic coupler 300, according to oneembodiment described herein. In an embodiment, the adiabatic coupler 300is a known configuration for a 50/50 coupler, meaning that it dividesthe input signal evenly between two outputs. Further, the adiabaticcoupler 300 is robust to manufacturing variation in terms of bandwidth,but not in terms of phase difference between the output signals.

The adiabatic coupler 300 includes waveguide portions 310A-D. In anembodiment, these four waveguide portions do not have equal width. Forexample, as illustrated in FIG. 3, the waveguide portions 310A and 310Beach have approximately the same width relative to each other: w_(s).The waveguide portions 310C and 310D do not have the same width relativeto each other. The waveguide portion 310C has a width w₂ and thewaveguide portion 310D has a width w₁, where w₁ and w₂ are differentwidths.

In an embodiment, an input signal 302 enters the adiabatic coupler andpasses through the waveguide portions 310A-D. This generates outputsignals 322 and 324. The output signals 322 and 324 represent anapproximately equal division of the power of the input signal 302. Asdiscussed above, this configuration is robust to manufacturing variationin terms of bandwidth. That is, the adiabatic coupler 300 divides theinput signal 302 approximately equally across a broad spectrum ofcommunication channels, regardless of minor manufacturing variances(e.g., to variation in silicon thickness).

The adiabatic coupler 300 is not, however, robust to manufacturingvariation in terms of phase difference. The phase difference between theoutput signal 322 and the output signal 324 varies based on numerousfactors, including the widths of the waveguide portions 310C and 310D,the gap between the waveguide portions 310C and 310D, and other factors.Because of this, manufacturing variance that changes these factors(e.g., variations in silicon thickness) change the phase differencebetween the output signals 322 and 324.

FIG. 4 illustrates a further adiabatic coupler 400, according to oneembodiment described herein. In an embodiment, the adiabatic coupler 400is also a 50/50 coupler, meaning that it divides the input signal evenlybetween two outputs. The adiabatic coupler 400, however, is robust tomanufacturing variation in terms of both bandwidth and phase differencebetween the output signals.

The adiabatic coupler 400 includes waveguide portions 410A-D. Here,these four waveguide portions 410A-D do not have equal widths. Forexample, as illustrated in FIG. 4, the waveguide portions 410C and 410Deach have approximately the same width relative to each other, w_(s),but the waveguide portions 410A and 410B do not have the same widthrelative to each other. The waveguide portion 410A has a width w₂ andthe waveguide portion 410B has a width w₁, where w₁ and w₂ are differentwidths.

In operation, an input signal 402 enters the adiabatic coupler andpasses through the waveguide portions 410A-D. This generates outputsignals 422 and 424. In an embodiment, the output signals 422 and 424represent an approximately equal division of the input signal 402.Further, the adiabatic coupler 400 is robust to manufacturing variation(e.g., variation in thickness) across bandwidths. The output signals 422and 424 represent an approximately equal division of the power of theinput signal 402 across a broad spectrum of communication channels.

The adiabatic coupler 400 is also robust to manufacturing variation interms of phase difference between output signals. This is because, inthe adiabatic coupler 400, the unequal width waveguide portions 410A and410B are on the input side of the coupler and the equal width waveguideportions 410C and 410D are on the output side of the coupler. Thisarrangement is different from the adiabatic coupler 300, illustrated inFIG. 3, in which the equal width waveguide portions 310A and 310B are onthe input side of the coupler and the unequal width waveguide portions310C and 310D are on the output side. Because of this difference, thephase difference between the output signal 422 and the output signal 424is a constant π/2 regardless of manufacturing variation (e.g., variationin thickness). As long as the symmetry is maintained (e.g., with anequal width of the output waveguide portions 410C and 410D), the phasedifference will be equal to π/2 due to the conversation of energyproperty in the unitary scattering matrix.

FIG. 5 illustrates a tap coupler device 500, according to one embodimentdescribed herein. As discussed above, the adiabatic coupler 400illustrated in FIG. 4 is generally robust to manufacturing variation inboth bandwidth and phase difference. But it is a 50/50 coupler, meaningthat it divides the power of the input signal evenly between twooutputs. The tap coupler device 500 illustrated in FIG. 5 is robust tomanufacturing variation in both bandwidth and phase difference, and isalso capable of dividing input signal power in any desired mannerbetween outputs.

In an embodiment, the tap coupler device 500 is configured to receive aninput signal 502 and to couple that signal to output signals 522 and524. The tap coupler device 500 includes two adiabatic couplers 530 and550, and phase delays 540A-B. For example, the adiabatic coupler 530that receives the input signal 502 can be the adiabatic coupler 300illustrated in FIG. 3, while the adiabatic coupler 550 that outputs theoutput signals 522 and 524 can be the adiabatic coupler 400 illustratedin FIG. 4. As discussed above with regard to FIG. 1C, the phase delays540A-B can be any suitable phase shifter (e.g., a phase shifter suitablefor use with known MZI based tap couplers).

The adiabatic coupler 530, on the input side of the tap coupler device500, includes four waveguide portions 532, 534, 536, and 538. The inputside waveguide portions 532 and 534 are approximately equal width, whilethe output side waveguide portions have different widths relative toeach other. The adiabatic coupler 550, on the output side of the tapcoupler device 500, includes four waveguide portions 552, 554, 556, and558. The input side waveguide portions 552 and 554 have different widthsrelative to each other. As illustrated in FIG. 5, the input waveguideportion 552 is wider than the input waveguide portion 554. The outputside waveguide portions 556 and 558 have approximately the same widthrelative to each other.

In an embodiment, the tap coupler device 500 includes only one phasedelay (e.g., either the phase delay 540A or the phase delay 540B). Forexample, the tap coupler device 500 can include only the phase delay540A. In this embodiment, the input side waveguide portion 552 of theadiabatic coupler 550 is optically coupled to the output side waveguideportion 536 of the adiabatic coupler 530, through the phase delay 540A.The input side waveguide portion 554 of the adiabatic coupler 550 isoptically coupled directly to the output side waveguide portion 538 ofthe adiabatic coupler 530. Alternatively, as discussed above, the tapcoupler device 500 can include both phase delays 540A-B and the inputside waveguide portion 554 of the adiabatic coupler 550 can be opticallycoupled to the output side waveguide portion 538 of the adiabaticcoupler 530 through the phase delay 540B.

In an embodiment, the tap coupler device 500 is robust to manufacturingvariation in terms of bandwidth, because it uses the adiabatic couplers530 and 550. As discussed above in relation to FIGS. 3 and 4, theseadiabatic couplers are generally robust to manufacturing variation interms of bandwidth. Further, the configuration of tap coupler device 500(e.g., the use of the two adiabatic couplers 530 and 550 with the phasedelays 540A-B) allows for any desired division of the power of the inputsignal 502 between the output signals 522 and 524. That is, unlike theadiabatic coupler 300 illustrated in FIG. 3 and the adiabatic coupler400 illustrated in FIG. 4, the power of the input signal 502 can bedivided in any way desired, not just 50/50 between the output signals.

Further, because the waveguide portions 556 and 558 (i.e., the finalwaveguide portions on the output side of the adiabatic coupler 550) haveapproximately equal width relative to each other, the phase differencebetween the output signals 522 and 524 is robust to manufacturingvariation and is generally constant at π/2. Thus, the tap coupler device500 is robust to manufacturing variation in terms of both bandwidth andphase difference between output signals, while allowing for any desireddivision of output signals.

In particular, the phase difference between the output signals 522 and524 is generally robust to variation in the silicon thickness whenmanufacturing the tap coupler device 500 and forming its components.This is particularly beneficial because manufacturing variation insilicon thickness can otherwise be difficult to cure. Some manufacturingprocess variations can be corrected using known processes, like OpticalProximity Correction (OPC). For example, width and gap variations indevices created during manufacturing can typically be corrected by OPC.But variations in the silicon thickness from forming the tap couplerdevice 500 (e.g., from forming the adiabatic couplers 530 and 550) cangenerally not be cured by OPC. The tap coupler device 500 alleviatesthis problem because these manufacturing variations in silicon thicknessdo not affect the phase difference in the output signals.

Instead, the design of the tap coupler device 500 ensures that the phasedifference between output signals 522 and 524 remains π/2, despitevariations in the silicon thickness of the manufactured adiabaticcouplers. In an embodiment, this is because output side waveguideportions 556 and 558 are approximately the same width relative to eachother. In an embodiment, the width margin can depend on the designrequirements for a particular tap coupler device (e.g., the budget,design requirements, specifications, etc.). This design keeps the phasedifference between the output signals 522 and 524 at π/2.

Further, just as this design makes the tap coupler device 500 lesssensitive to manufacturing variations in silicon thickness, the designalso makes the tap coupler device 500 less sensitive to width and gapvariations from manufacturing. While these variations may be correctedusing OPC and other known processes, as discussed above, the tap couplerdevice 500 allows for improved manufacturing (e.g., cheaper and faster)because it mitigates the need for correction using OPC.

The designs illustrated in FIG. 5, and related embodiments (e.g., FIGS.6 and 7 below) are fully passive in terms of phase difference betweenoutput signals. In some known devices, active tuning is used to modifythe phase difference between output signals in case of manufacturingvariation. In the tap coupler device 500, the phase difference betweenthe output signals 522 and 524 is constant at π/2 and no active tuningis required. This further saves power and results in an improved productthat is cheaper and easier to configure.

FIG. 6 illustrates a further tap coupler device 600, according to oneembodiment described herein. In an embodiment, the tap coupler device600 is similar to the tap coupler device 500 illustrated in FIG. 5 insome ways. For example, the tap coupler device 600 includes twoadiabatic couplers, 630 and 650, and phase delays 640A-B. Further, theinput side waveguide portions 652 and 654, in the adiabatic coupler 650,have different widths relative to each other (e.g., similar to the inputside waveguide portions 552 and 554 illustrated in FIG. 5).

In the adiabatic coupler 650, however, the waveguide portion 652,coupled to the phase delay 640A, is wider than the waveguide portion654. In the adiabatic coupler 550 illustrated in FIG. 5, the input sidewaveguide portion 552, coupled to the phase delay 540A, is narrower thanthe waveguide portion 554. This variation preserves the advantages ofthe tap coupler device 600 (e.g., robustness to manufacturing variationand uneven division of signal power), but allows for improvedperformance in certain applications.

In an embodiment, the tap coupler device 600 includes only one phasedelay (e.g., either the phase delay 640A or the phase delay 640B). Forexample, the tap coupler device 600 can include only the phase delay640A. In this embodiment, the input side waveguide portion 652 of theadiabatic coupler 650 is optically coupled to the output side waveguideportion 636 of the adiabatic coupler 630, through the phase delay 640A.The input side waveguide portion 654 of the adiabatic coupler 650 isoptically coupled directly to the output side waveguide portion 638 ofthe adiabatic coupler 630. Alternatively, as discussed above, the tapcoupler device 600 can include both phase delays 640A-B and the inputside waveguide portion 654 of the adiabatic coupler 650 can be opticallycoupled to the output side waveguide portion 638 of the adiabaticcoupler 630 through the phase delay 640B.

A person of ordinary skill in the art can select between the tap couplerdevice 500 and the tap coupler device 600, depending on the desiredapplication. In an embodiment, the choice between the tap coupler device500 and the tap coupler device 600 can depend on the implementation ofwidth transition design and phase delay design. For example, in the tapcoupler device 500, width transition may be required between 536 and552, and between 538 and 554, due to the width mismatch. In tap couplerdevice 600, width transition is not required due to the equal widthbetween 636 and 652, and between 638 and 654. However, in the tapcoupler device 600, the phase delay design may need to compensate for aphase difference induced by the mismatch of waveguide width between theupper arm (wider waveguides 636/652) and the lower arm (narrowerwaveguides 638/654).

As discussed above, the tap coupler device 600 includes two adiabaticcouplers 630 and 650, and phase delays 640A-B. The adiabatic coupler 650is oriented so that waveguide portions having the same width, relativeto each other, are on the output side of the tap coupler device 600. Forexample, the adiabatic coupler 630 includes four waveguide portions 632,634, 636, and 638. The input side waveguide portions 632 and 634 have anapproximately equal width, relative to each other, while the output sidewaveguide portions have different widths, relative to each other. Theadiabatic coupler 650 also includes four waveguide portions 652, 654,656, and 658. The input side waveguide portions 652 and 654 havedifferent widths, relative to each other, while the output sidewaveguide portions 656 and 658 have approximately the same width,relative to each other.

An input signal 602 passes through the first adiabatic coupler 630. Theinput signal 602 then passes through one (or both) of the phase delays640A-B. As discussed above with regard to FIG. 1C, the phase delays640A-B can be any suitable phase shifter (e.g., a phase shifter suitablefor use with a known MZI based tap coupler). The input signal thenpasses through the adiabatic coupler 650, generating two output signals622 and 624.

Like the tap coupler device 500 illustrated in FIG. 5, the tap couplerdevice 600 allows for any desired division of power between the outputsignals 622 and 624. That is, the power of the input signal 602 can bedivided in any way desired, not just 50/50 between the output signals.Further, again like the tap coupler device 500 illustrated in FIG. 5,because the waveguide portions 656 and 658 (i.e., the final waveguideportions on the output side of the adiabatic coupler 650) haveapproximately equal width, the phase difference between the outputsignals 622 and 624 is π/2.

As discussed above with regard to FIG. 5, for the tap coupler device 600the output phase difference between the output signals 622 and 624 doesnot depend on manufacturing process variations in the adiabatic couplers630 and 650. For example, the silicon thickness in the adiabaticcouplers 630 and 650 may vary across different manufactured deviceswithout any significant difference in the respective phase differences.The design of the tap coupler device 600 ensures that the phasedifference between output signals 622 and 624 remains π/2, despitevariations in the silicon thickness of the manufactured adiabaticcouplers.

In various embodiments, the tap coupler device 500 illustrated in FIG. 5and the tap coupler device 600 illustrated in FIG. 6 are operable acrossa number of communication bands. For example, these tap coupler designsare generally operable in either the C-band or the O-band. As is knownto a person of ordinary skill, however, variations in material andparameters may make a particular tap coupler more suitable for onecommunication band or another. For example, the tap coupler device 500may be more suitable for one communication band, while the tap couplerdevice 600 may be more suitable for a different communication band.

FIG. 7 illustrates a top down view of a structure for a tap couplerdevice 700, according to one embodiment described herein. In anembodiment, the tap coupler device 700 illustrates additional detailsabout the tap coupler device 600 illustrated in FIG. 6. Like the tapcoupler device 600, the tap coupler device 700 is generally robust tomanufacturing variation in terms of both bandwidth and phase difference,and allows for any desired division of output signals.

In an embodiment, the tap coupler device 700 may use two core opticalguiding materials: Silicon (Si) and Silicon Oxynitride (SiON).Regardless of the core optical guiding material, oxide may be used as acladding material. While the illustrated Figure is discussed in terms ofthese materials, other suitable materials can also be used instead of,or in addition to, Si an SiON. For example, Silicon Nitride (Si₃N₄)could be used in place of, or in addition to, SiON and Si.

Si is commonly used as an optical guiding/routing material in theintegrated optics industry. In general, Si allows for relativelyseamless integration, and compatibility, for most platforms. Comparedwith Si, SiON typically has weaker optical refinement and is lesssensitive to the wave-guiding geometry. Therefore, SiON is more robustto manufacturing process variation induced geometry changes (e.g., towidth, gap, height, etc.). Further, the refractive index of SiON isgenerally insensitive to temperature. This allows high tolerance intemperature variation in the transceiver module, and does not requireactive tuning to balance the temperature variation. This conserves powerand helps reduce the power budget for devices incorporating SiON.

Si and SiON can each be particularly suitable for differentapplications. Taking the configurations illustrated in FIGS. 5 and 6 asexamples, for some applications it is preferable to use SiON for bothphase delay (e.g., phase delays 540A-B and 640A-B) and the adiabaticcouplers (e.g., the adiabatic couplers 530, 550, 630, and 650). Thisfacilitates an all passive device (e.g., that does not include anyactive tuning components), that has a high tolerance to temperaturevariation and is robust to process variation.

For other applications, it is preferable to use Si. Taking theconfigurations illustrated in FIGS. 5 and 6 as examples, again, Si canbe used for both phase delay (e.g., phase delays 540A-B and 640A-B) andthe adiabatic couplers (e.g., the adiabatic couplers 530, 550, 630, and650). This allows for relatively easy and effective turning of thedevice, with a trade-off in tolerance to temperature variation androbustness to manufacturing variation. This is a good alternative forsome applications.

Finally, for other applications, it is preferable to use a combinationof SiON and Si. For example, again referring to FIGS. 5 and 6, SiONcould be used in the adiabatic couplers (e.g., the adiabatic couplers530, 550, 630, and 650) and Si can be used in the phase delay (e.g.,phase delays 540A-B and 640A-B). This combination configurationgenerally balances the benefits of both materials, and is a goodsolution for most applications. Further, as discussed above, othermaterials could be used. For example, Si₃N₄ could be used in place of,or in addition to, SiON and Si.

FIG. 7 illustrates one embodiment of a combination SiON and Siconfiguration. As discussed above, in an embodiment, the tap couplerdevice 700 provides one example structure for the tap couplerillustrated in FIG. 6. This is merely one example, however, and otherstructures can be used, for the tap coupler device 600 illustrated inFIG. 6 and the other tap couplers illustrated in FIGS. 1-5 (e.g., thetap coupler device 500 illustrated in FIG. 5).

The tap coupler device 700 includes two adiabatic couplers 730 and 750(e.g., corresponding to the adiabatic couplers 630 and 650 illustratedin FIG. 6). The tap coupler device 700 further includes a phase delay740 (e.g., corresponding to the phase delays 640A-B illustrated in FIG.6). The adiabatic couplers 730 and 750 are coupled to the phase delay740 using bending components B1 and B2 and taper components T1, T2, andT3.

The tap coupler device 700 further includes an upper arm 710 and a lowerarm 720. The upper arm 710 optically couples the adiabatic coupler 730to the phase delay 740, and the phase delay 740 to the adiabatic coupler750. The lower arm 720 optically couples the adiabatic coupler 730 tothe adiabatic coupler 750. In an embodiment, the same set of tapers areused in the upper arm 710 and the lower arm 720. That is, as illustratedin FIG. 7, tapers T1 and T3 are used both in the upper arm 710 and thelower arm 720, but in reverse order (e.g., the taper T3 is on the inputside in the upper arm while the taper T1 is on the input side in thelower arm). These tapers include approximately equal dimensions.

In an embodiment, the phase delay 740 is implemented using twowaveguides. The upper arm 710 includes a waveguide with a width W₁. Thelower arm 720 includes a waveguide with a width W₂. As illustrated inFIG. 7, the waveguides in the upper arm 710 and the lower arm 720 havethe same length: L. In an embodiment, the widths at the points where thebends B1 and B2 meet the tapers T1 and T3 can vary. These are labeled asW_(A) and W_(B).

As discussed above, in an embodiment the adiabatic couplers 730 and 750can use Si, SiON, or any other suitable material as the core opticalguiding material. Similarly, the phase delay 740 can include Si, SiON,or any other suitable material as the core optical guiding material. Inone embodiment, the phase delay 740 uses Si as the core optical guidingmaterial while the adiabatic couplers 730 and 750 use SiON as the coreoptical guiding material. As discussed above, this configurationprovides for a balance of benefits between the materials and is suitablefor many applications.

In the current disclosure, reference is made to various embodiments.However, the scope of the present disclosure is not limited to specificdescribed embodiments. Instead, any combination of the describedfeatures and elements, whether related to different embodiments or not,is contemplated to implement and practice contemplated embodiments.Additionally, when elements of the embodiments are described in the formof “at least one of A and B,” it will be understood that embodimentsincluding element A exclusively, including element B exclusively, andincluding element A and B are each contemplated. Furthermore, althoughsome embodiments disclosed herein may achieve advantages over otherpossible solutions or over the prior art, whether or not a particularadvantage is achieved by a given embodiment is not limiting of the scopeof the present disclosure. Thus, the aspects, features, embodiments andadvantages disclosed herein are merely illustrative and are notconsidered elements or limitations of the appended claims except whereexplicitly recited in a claim(s). Likewise, reference to “the invention”shall not be construed as a generalization of any inventive subjectmatter disclosed herein and shall not be considered to be an element orlimitation of the appended claims except where explicitly recited in aclaim(s).

As will be appreciated by one skilled in the art, the embodimentsdisclosed herein may be embodied as a system, method or computer programproduct. Accordingly, embodiments may take the form of an entirelyhardware embodiment, an entirely software embodiment (includingfirmware, resident software, micro-code, etc.) or an embodimentcombining software and hardware aspects that may all generally bereferred to herein as a “circuit,” “module” or “system.” Furthermore,embodiments may take the form of a computer program product embodied inone or more computer readable medium(s) having computer readable programcode embodied thereon.

Program code embodied on a computer readable medium may be transmittedusing any appropriate medium, including but not limited to wireless,wireline, optical fiber cable, RF, etc., or any suitable combination ofthe foregoing.

Computer program code for carrying out operations for embodiments of thepresent disclosure may be written in any combination of one or moreprogramming languages, including an object oriented programming languagesuch as Java, Smalltalk, C++ or the like and conventional proceduralprogramming languages, such as the “C” programming language or similarprogramming languages. The program code may execute entirely on theuser's computer, partly on the user's computer, as a stand-alonesoftware package, partly on the user's computer and partly on a remotecomputer or entirely on the remote computer or server. In the latterscenario, the remote computer may be connected to the user's computerthrough any type of network, including a local area network (LAN) or awide area network (WAN), or the connection may be made to an externalcomputer (for example, through the Internet using an Internet ServiceProvider).

Aspects of the present disclosure are described herein with reference toflowchart illustrations and/or block diagrams of methods, apparatuses(systems), and computer program products according to embodimentspresented in this disclosure. It will be understood that each block ofthe flowchart illustrations and/or block diagrams, and combinations ofblocks in the flowchart illustrations and/or block diagrams, can beimplemented by computer program instructions. These computer programinstructions may be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create means for implementing thefunctions/acts specified in the block(s) of the flowchart illustrationsand/or block diagrams.

These computer program instructions may also be stored in a computerreadable medium that can direct a computer, other programmable dataprocessing apparatus, or other device to function in a particularmanner, such that the instructions stored in the computer readablemedium produce an article of manufacture including instructions whichimplement the function/act specified in the block(s) of the flowchartillustrations and/or block diagrams.

The computer program instructions may also be loaded onto a computer,other programmable data processing apparatus, or other device to cause aseries of operational steps to be performed on the computer, otherprogrammable apparatus or other device to produce a computer implementedprocess such that the instructions which execute on the computer, otherprogrammable data processing apparatus, or other device provideprocesses for implementing the functions/acts specified in the block(s)of the flowchart illustrations and/or block diagrams.

The flowchart illustrations and block diagrams in the Figures illustratethe architecture, functionality, and operation of possibleimplementations of systems, methods, and computer program productsaccording to various embodiments. In this regard, each block in theflowchart illustrations or block diagrams may represent a module,segment, or portion of code, which comprises one or more executableinstructions for implementing the specified logical function(s). Itshould also be noted that, in some alternative implementations, thefunctions noted in the block may occur out of the order noted in theFigures. For example, two blocks shown in succession may, in fact, beexecuted substantially concurrently, or the blocks may sometimes beexecuted in the reverse order, depending upon the functionalityinvolved. It will also be noted that each block of the block diagramsand/or flowchart illustrations, and combinations of blocks in the blockdiagrams and/or flowchart illustrations, can be implemented by specialpurpose hardware-based systems that perform the specified functions oracts, or combinations of special purpose hardware and computerinstructions.

In view of the foregoing, the scope of the present disclosure isdetermined by the claims that follow.

We claim:
 1. An optical communication device, comprising: a phase delay;and an adiabatic coupler, comprising: a first output and a secondoutput; a first waveguide comprising a first portion optically coupledto the first output and a second portion adapted to be optically coupledto the phase delay; and a second waveguide comprising a third portionoptically coupled to the second output and a fourth portion adapted tobe optically coupled to an output of another adiabatic coupler, whereinthe first portion comprises a first width and the third portioncomprises a second width approximately equal to the first width, whereinthe adiabatic coupler is configured to produce a first output signalusing the first output and a second output signal using the secondoutput, with a constant relative phase difference between the firstoutput signal and the second output signal, and wherein the adiabaticcoupler is configured to divide an input signal to the opticalcommunication device in an uneven power distribution between the firstoutput signal and the second output signal.
 2. The optical communicationdevice of claim 1, the phase delay comprising: a first arm comprising afirst phase-delay waveguide, the phase-delay waveguide comprising afirst phase-delay width and a first phase-delay length; and a second armcomprising a second phase-delay waveguide, the second phase-delaywaveguide comprising a second phase-delay width different from the firstphase-delay width and a second phase-delay length approximately equal tothe first phase-delay length.
 3. The optical communication device ofclaim 2, wherein the first arm comprises first and second tapercomponents, the second arm comprises third and fourth taper components,the third taper component comprises dimensions approximately equal tothe first taper component, and the fourth taper component comprisesdimensions approximately equal to the second taper component.
 4. Theoptical communication device of claim 1, wherein the another adiabaticcoupler is adapted to receive the input signal and adapted to beoptically coupled to an input of the phase delay.
 5. The opticalcommunication device of claim 1, wherein the second width is equal tothe first width.
 6. The optical communication device of claim 1,wherein: the first waveguide further comprises a third portion adaptedto be optically coupled to the output of the phase delay and comprisinga third width, and the second waveguide further comprises a fourthportion adapted to be optically coupled to the another adiabatic couplerand comprising a fourth width.
 7. The optical communication device ofclaim 6, wherein the third width is not equal to the fourth width. 8.The optical communication device of claim 7, wherein the third width isless than the fourth width.
 9. The optical communication device of claim1, wherein the adiabatic coupler comprises at least one of SiliconOxynitride (SiON) or Silicon Nitride (Si₃N₄) as a first optical guidingmaterial and wherein the phase delay comprises Silicon (Si) as a secondoptical guiding material.
 10. The optical communication device of claim1, wherein the phase delay comprises a passive phase delay.
 11. Theoptical communication device of claim 10, wherein the phase delaycomprises Si as an optical guiding material.
 12. An adiabatic coupler,comprising: a first output and a second output; a first waveguidecomprising a first portion optically coupled to the first output and asecond portion adapted to be optically coupled to a phase delay; and asecond waveguide comprising a third portion optically coupled to thesecond output and a fourth portion adapted to be optically coupled to anoutput of another adiabatic coupler, wherein the first portion comprisesa first width and the third portion comprises a second widthapproximately equal to the first width, wherein the adiabatic coupler isincluded in an optical communication device, wherein the adiabaticcoupler is configured to produce a first output signal using the firstoutput and a second output signal using the second output, with aconstant relative phase difference between the first output signal andthe second output signal, and wherein the adiabatic coupler isconfigured to divide an input signal to the optical communication devicein an uneven power distribution between the first output signal and thesecond output signal.
 13. The adiabatic coupler of claim 12, wherein theanother adiabatic coupler is adapted to receive the input signal andadapted to be optically coupled to an input of the phase delay.
 14. Theadiabatic coupler of claim 12, wherein the second width is equal to thefirst width.
 15. The adiabatic coupler of claim 12, wherein: the firstwaveguide further comprises a third portion adapted to be opticallycoupled to the output of the phase delay and comprising a third width,and the second waveguide further comprises a fourth portion adapted tobe optically coupled to the another adiabatic coupler and comprising afourth width, and wherein the third width is not equal to the fourthwidth.
 16. The adiabatic coupler of claim 12, wherein the adiabaticcoupler comprises at least one of Silicon Oxynitride (SiON) or SiliconNitride (Si₃N₄) as a first optical guiding material and wherein thephase delay comprises Silicon (Si) as a second optical guiding material.17. The adiabatic coupler of claim 12, wherein the phase delay comprisesa passive phase delay.
 18. A fiber optic communication system,comprising: a data source; a multiplexer; a demultiplexer; and a tapcoupler comprising: a phase delay; and an adiabatic coupler, comprising:a first output and a second output; a first waveguide comprising a firstportion optically coupled to the first output and a second portionadapted to be optically coupled to the phase delay; and a secondwaveguide comprising a third portion optically coupled to the secondoutput and a fourth portion adapted to be optically coupled to an outputof another adiabatic coupler, wherein the first portion comprises afirst width and the third portion comprises a second width approximatelyequal to the first width, wherein the adiabatic coupler is configured toproduce a first output signal using the first output and a second outputsignal using the second output, with a constant relative phasedifference between the first output signal and the second output signal,and wherein the adiabatic coupler is configured to divide an inputsignal to the tap coupler in an uneven power distribution between thefirst output signal and the second output signal.
 19. The fiber opticcommunication system of claim 18, wherein the adiabatic couplercomprises at least one of Silicon Oxynitride (SiON) or Silicon Nitride(Si₃N₄) as a first optical guiding material and wherein the phase delaycomprises Silicon (Si) as a second optical guiding material.
 20. Thefiber optic communication system of claim 18, wherein the phase delaycomprises a passive phase delay.